1. Field of the Invention
The present invention relates to a high definition image generating system for an image processing apparatus which converts multi-level data into dot impact output data of font patterns.
2. Description of the Prior Art
A digital copying machine reads an image on an original document, converts the resultant analog signal into a multi-level data, performs image-quality adjustment processings, such as the adjustments of granular, tone, and definition, and reproduces the original image in the form of a mesh-dot image. In the digital copying machine, the multi-level data as digital data is used for the data processing to generate a high definition image. Because of this, various types of edits can be done using the digital data and a memory.
FIG. 11 is a block diagram showing an arrangement of a digital copying machine.
In FIG. 11 , an IIT (image input terminal) 100 reads an image on a color original document in the form of separated three primary colors, B (blue), G (green), and R (red) by using a CCD line sensor, and converts the separated three color signals into digital image data. An IOT (image output terminal) 115 performs the exposure by a laser beam, and the development, and reproduces the original color image. Various processing units ranging from an END converter 101 to an IOT interface 110, which are located between the IIT 100 and the IOT 115, make up a system for editing image data, i.e., an image processing system (IPS). In the edit processing system, the image data of B, G and R are converted into toner color data of Y (yellow), M (magenta), and C (cyan), and K (black or India ink), and every developing cycle produces a toner signal corresponding to the developing color. When the separated color signals (B, G, and R signals) are converted into toner signals (Y, M, C, and K signals), the following items become problematic; how to adjust color balance, how to reproduce the colors in conformity with the read characteristic of the IIT and the output characteristic of the IOT, how to adjust the balance between density and contrast, and how to adjust edge emphasis, blur and Moire, and the like.
The IIT reads the original image, by using a CCD line sensor, with the size of 16 dots/mm for each pixel for the respective colors B, G and R, and outputs the data of 24 bits (3 colors.times.8 bits; 256 gray levels). The CCD line sensor is coupled with color filters of B, G, and R, and has a length of 300 mm at a density of 16 dots/mm, and makes a scan of 16 lines/mm at a process speed of 190.5 mm/sec. Therefore, it produces read data at a speed of approximately 15M pixels/sec. for each color. In the IIT, the analog data of B, G and R pixels is subjected to the logarithmic conversion. As the result of the conversion, the reflectivity information is transformed into density information, and further to digital data.
The IPS receives the separated color signals of B, G and R from the ITT, and executes various data processings to improve color reproduction, tone reproduction, definition reproduction, and the like, converts the toner signals of the developing process colors into on/off signals, and outputs them to the IOT. the IPS is made up of various types of modules; an END (equivalent neutral density) conversion module 101 for adjusting (converting) the color signals to a gray-balanced color signals, a color masking module 102 for converting the color signals B, G and R into toner quantity signals of Y, M and C by matrix-calculating the signals of B, G and R, a document-size detecting module 103 for detecting the document size in a prescan mode and erasing (frame-erasing) a platen color in a scan mode, a color conversion module 104 for converting a color in a designated area into another color according to an area signal that is applied from an area image control module, a UCR (under color removal) & black generating module 105 which generates black K of such a proper quantity as to prevent impure color, equally reduces colors of Y, M, C according to the quantity of K, removes the under color of the K, and Y, M, and C according to signals of the monocolor mode and 4-pass full color mode, a spatial filter 106 capable of removing blur and Moire, a TRC (tone reproduction control) for density adjustment, contrast adjustment, negative/positive inversion, color balance, and the like in order to improve the reproduction performance, a screen generator 109 for converting the tone toner signals of the process colors into on/off or 2-level toner signal, an IOT interface module 110, the area image control module 111 including an area generating circuit and a switch matrix, and an edit control module including an area command memory 112, a color palette video switch circuit 113, and font buffer 114, and the like.
For the separated color signals of B, G, and R from the IIT, 8-bit data (256 gray levels) is inputted to the END conversion module 101 where those are converted into toner signals of Y, M, C and K. The toner signal X of the process color is selected and converted into 2-level signal. It is outputted as on/off data of the toner signal of the process color, from the IOT interface module 110 to the IOT. In the case of the full color (4-pass full color), through the prescan, a document size, an edit area and other document information are first collected. Then, a copy cycle is first executed with the toner signal X whose developing color is Y, for example. Another copy cycle is next executed with the toner signal X whose developing color is M. Subsequently, similar copy cycles are repeated for the four image readings.
In the copying machine as mentioned above, since the removal of mesh dots results in blur, a nonlinear spatial filter to emphasize the edge and a screen generator are combined to generate a high definition image. Use of the combination leads to increase of the hardware scale. Excessive emphasis of the edge brings about unnatural emphasis of the edge. This appears as discontinuity in the reproduced image. That is, the edge portion in the image is unnaturally emphasized or the details in the image are blurred. The image quality of the reproduced image is deteriorated. In such a case, when the generation copy is progressively repeated, the image quality deterioration is amplified and enlarged.